The Prime Minister finally has negotiated a final version of the agreement that withdraws the UK from the EU and sets the future relationship between the two. But the Brexit faction of the Tories hates it because they basically promised that the final agreement would be complete independence from the EU instead of what is likely to be dependence on EU rules on pretty much everything. It's very possible that the agreement might not pass Parliament because of this, which would raise the probability of a Hard Brexit, i.e. a complete break with the EU on Brexit Day 2019 and a probable economic and political catastrophe.